Link chains with chain links that are connected to one another by means of chain joints are in use in the state of the art in various forms. To a predominant extent, these are chains in which an inner chain link made of two parallel inner plates alternates with an outer chain link that consists of two outer plates connected to each other by means of two pins. A chain joint is thereby formed by means of a pin and the plates of the inner chain link which are pivotable on said pin. In the event that the chain has bushings, the chain joint is formed by the bushing and the pin fed through and held in a pivotable manner.
In use as driving chains or conveyor chains, particularly the area of the chain joint is highly loaded so that there is a great demand here with respect to a wear-resistant bearing surface. In addition to the use as driving chains or conveyor chains, link chains are again increasingly being used in the automotive industry for controlling the valve operating mechanism of internal combustion engines. The requirements on the wear resistance are thereby particularly high, because in internal combustion engines there are very frequent load-cycle changes and only very restricted access for maintenance or replacement of the chain. Moreover, there is an endeavour to design the chain so that it is as small and has as little weight as possible, which further increases the load on the individual chain elements.
In order to achieve the necessary wear resistance and to avoid elongation caused by wear, the pins and/or bushings of conventional link chains are subjected to heat treatment, e.g., hardening and tempering, carbonisation, carbonitriding, etc., or they are provided with a carbide layer. In spite of heat treatment of the joint components and/or the formation of a carbide layer on the joint surfaces, wear problems and elongation caused by wear occur, particularly in the use as timing chains in an internal combustion engine, that reduce the engine's reliability or necessitate an expensive exchange of the chain.
A link chain of this category is known from DE 10 2006 052 869 A1. In this, a link chain is disclosed whose pin and/or bushing is provided with a PVD hard material layer, whereby the pin and/or the bushing consists of a base material made of a high carbon steel with a carbon content between 0.4 weight % and 1.2 weight % that supports the PVD hard material layer. The disclosed PVD hard material layer can consist both of metal hard materials and of non-metal hard materials. All carbides, nitrides, carbonitrides, borides, and silicides of the transition metals come into question as metal hard materials. Coming into question as non-metal hard materials are, for example, diamond and DLC (diamond-like carbon), as well as corundum, boron carbide, cubic boron nitride, silicon carbide or aluminium nitride.
Such hard material layers represent an improvement over the previously used coating methods. Nevertheless, due to the aforementioned high loads and the trend towards smaller dimensioning of engines with simultaneous power increase, there is a demand for chains capable of bearing even greater loads.
PVD methods furthermore have the problem that the coating material deposits not only on the objects to be coated, but also in the coating system. In the case of the PVD method (Physical Vapour Deposition), so-called targets are used that consist of the material that is to be deposited on the component to be coated. By means of different methods, it is possible to separate the coating material from this target so that it arrives as a gaseous particle flow on the surface of the component to be coated and forms a coating. Here it is wished, on the one hand, that the targets consist only of the elements that later should also be deposited on the end product. Moreover, one objective is to keep the material combinations that later are deposited on the end product at a low number. This simplifies the assembly or production of the targets and consequently also minimizes the complexity of the unwanted contamination of the coating chamber.